A. Field of the Invention
The present invention relates generally to photonic crystals, and, more particularly to multi-channel wavelength division multiplexing using photonic crystals.
B. Description of the Related Art
During the last decade photonic crystals (also known as photonic band-gap materials) have risen from an obscure technology to a prominent field of research. In large part this is due to their unique ability to control, or redirect, the propagation of light. E. Yablonovich, “Inhibited spontaneous emission in solid-state physics and electronics,” Physical Review Letters, vol. 58, pp. 2059-2062 (May 1987), and S. John, “Strong localization of photons in certain disordered dielectric superlattices,” Physical Review Letters, vol. 58, pp. 2486-2489 (June 1987), initially proposed the idea that a periodic dielectric structure can possess the property of a band gap for certain frequencies in the electromagnetic spectra, in much the same way as an electronic band gap exists in semiconductor materials. This property affords photonic crystals with a unique ability to guide and filter light as it propagates within it. Thus, photonic crystals have been used to improve the overall performance of many optoelectronic devices.
The concept of a photonic band gap material is as follows. In direct conceptual analogy to an electronic band gap in a semiconductor material, which excludes electrical carriers having stationary energy states within the band gap, a photonic band gap in a dielectric medium excludes stationary photonic energy states (i.e., electromagnetic radiation having some discrete wavelength or range of wavelengths) within that band gap. In semiconductors, the electronic band gap results as a consequence of having a periodic atomic structure upon which the quantum mechanical behavior of the electrons in the material must attain eigenstates. By analogy, the photonic band gap results if one has a periodic structure of a dielectric material where the periodicity is of a distance suitable to interact periodically with electromagnetic waves of some characteristic wavelength that may appear in or be impressed upon the material, so as to attain quantum mechanical eigenstates.
A use of these materials that can be envisioned, is the optical analog to semiconductor behavior, in which a photonic band gap material, or a plurality of such materials acting in concert, can be made to interact with and control light wave propagation in a manner analogous to the way that semiconductor materials can be made to interact with and control the flow of electrically charged particles, i.e., electricity, in both analog and digital applications.
Photonic crystals have been used to improve the overall performance of many optoelectronic devices. The inventors of the present invention investigated the application of photonic crystals to a multi-channeled, wavelength-division multiplexed (WDM) device. The use of WDM in communication systems allows for better utilization of the spectral bandwidth resources available to the systems. Conventional WDM systems have been proposed using many different technologies, such as planar lightwave circuit (PLC)-based array waveguide gratings (AWGs), and fiber gratings. However, these conventional devices typically have sizes on the order of centimeters or meters, in order to support a large number of sufficiently-spaced wavelength channels. In contrast, photonic crystals enable a much larger number of channels on a much smaller scale. Thus, some conventional WDM devices based on photonic crystals have been proposed. However, these devices are based on the superprism phenomenon, as well as channel drop filters. The superprism phenomenon is the dispersion of light 500 times stronger than the dispersion of light in conventional prisms. A channel drop filter is a device which picks out a small range of frequencies from a waveguide and reroutes it in another direction, leaving the other frequencies unaffected. These conventional WDM devices fail to maximize the density of frequency-selective channels, and thus, fail to maximize usage of the available bandwidth of the photonic crystals.
Thus there is a need in the art to provide a WDM device that maximizes the density of frequency-selective channels, which thereby maximizes usage of the available bandwidth of the photonic crystals.